The name assigned to the last mission was "Operation Avenger". I doubt that name was randomly generated.
There's an achievement - Edison - for completing every single research project. At the end of the game, I had no research projects available. I completed every dissection (there's an achievement for that), and I interrogated every single biological alien except for the chrysalid (which can't be stunned). And yet I somehow didn't get the Edison achievement. Clearly, I missed something, though I'm not sure what. Maybe there's an alien device that turns up when the aliens escalate things further?
There are several "hidden" achievements that I'm utterly clueless about. The only reason that I know they exist is because they show up on Steam's list of "percentage of players who have earned each achievement". Typically such achievements are hidden due to plot-related reasons, but I've finished the game and those achievements are still unearned. In fact, as of last night, no one had earned the achievements in question, and almost all of the achievements had been earned at that point by at least 0.1% of the Steam XCom playerbase (there were a few others that were still unearned, but they were the extremely difficult ones). Additionally, locating the achievements on Achievement websites (there's a list at Neoseeker here - http://www.neoseeker.com/steam/xcom_enemy_unknown/
) provides an odd bit of help text for each of them (help text on secret achievements isn't displayed in Steam until after you earn the achievements) that in most cases seem to reference specific missions. Council missions that just haven't turned up yet? It seems as if *someone* would have received those missions by now. Future DLC with plot-filled missions? But DLC achievements are typically added when the DLC goes live, or shortly before. Or something else? Though I can't think of what. In any event, I'm very curious about these.
There's a little easter egg for old XCom fans when you research the Laser Rifle. There's a similar one when you manufacture your first Plasma Rifle (note that you need to build it for the easter egg, not just research it, and not capture it).